Communication system design is generally concerned with maximizing information transfer from a transmitter to a receiver along a noisy channel with acceptable reliability. In practice, the channel is often time-varying (e.g., a fading channel for wireless communication) in addition to being noisy. Provision of a complete description of the channel to the transmitter, for designing the signal to increase the transmission rate and reliability, is usually difficult in practice. Various approaches have been developed for communication on time-varying channels, where differing levels of channel description are provided to the transmitter. Typically, system complexity and information transfer rate both increase as the amount and quality of channel description provided to the transmitter is improved, resulting in a performance-complexity trade-off.
Provision of a channel description to the transmitter is especially valuable in multiple transmitter antenna systems, in contrast to single antenna systems. Multi-input, multi-output (MIMO) systems (including multi-input single-output systems as a special case) commonly use space-time block codes (e.g., as considered by Alamouti et al. in U.S. Pat. No. 6,185,258). However, conventional space-time block codes do not make use of channel description. Further information on space-time coding in MIMO systems is given by Gesbert et al. in an article “From Theory to Practice: an Overview of MIMO Space-Time Coded Wireless Systems”, IEEE J. Selected Areas in Communication 21(3) April 2003. Methods of utilizing channel description in multiple transmit-antenna systems, in combination with such codes, are presently under investigation, especially for wireless communication.
For example, use of a precoder derived from the channel transfer function in a MIMO system to eliminate inter-symbol interference is considered in US 2003/0235146 by Wu et al. In US 2001/0033622 by Jöngren et al., a channel description in the form of quantized feedback information is provided to the transmitter in a MIMO system and used to derive a linear preceding transformation. In US 2005/0048933 by Wu et al., a simplified feedback approach is considered, where 2(M−1) bits of feedback channel description are provided to a transmitter having M antennas in a MIMO system. Use of channel description information is sometimes known as “beamforming”. Beamforming in combination with orthogonal coding is considered in US 2002/0186779 and US 2003/0035490 by Gollamudi.
In some cases, the channel description is statistical. For example, in an article entitled “Linear Precoding for Space-Time Coded Systems with Known Fading Correlations”, IEEE Comm. Letters 6(6) June 2002, Sampath and Paulraj consider the use of a channel correlation matrix to derive an optimal linear precoder for a space-time coded system.
As indicated above, there is a trade-off between system performance (increasing channel description improves performance) and system complexity (increasing channel description increases complexity). In particular, approaches which attempt to provide an accurate instantaneous channel description to the transmitter are often difficult and/or complex to implement. Approaches which provide a statistical channel description to the transmitter are relatively simple to implement, but it appears that only single-parameter statistical channel descriptions (e.g., channel mean OR channel correlation) have been considered.
Accordingly, it would be an advance in the art to provide optimized linear preceding for a multi-input communication system based on a multi-parameter statistical description of the channel.